1. Field of the Invention
The field of the present invention is driven wheel torque control systems of a type including a torque converter provided between an internal combustion engine of a vehicle and a driven wheel, and a driven wheel torque reducing means for reducing an output torque of the driven wheel when slipping of the driven wheel becomes excessive.
2. Description of the Related Art
A method has been proposed in which an output torque from the internal combustion engine is estimated in a traction control system, and a torque of the driven wheel is estimated from this estimated output torque and a reduction ratio between the internal combustion engine and the driven wheel (see Japanese Patent Application Laid-open No. 31831/88).
Another method has been also proposed in which a driven wheel torque is found in consideration of an amount of torque amplified by the torque converter in a vehicle provided with an automatic transmission, and the driven wheel torque reducing means is operated when such driven wheel torque exceeds a predetermined value (see Japanese Patent Application Laid-open No. 148629/89).
A construction in the latter measure is such that a driven wheel output torque is calculated on the basis of a current input/output rotational speed ratio of the torque converter, and slipping of the driven wheel is inhibited when such driven wheel torque exceeds a required value. However, an actual slipping of the driven wheel is produced by a surplus portion of the driven wheel torque which is increased with an increase in output torque from the internal combustion engine, and there is a somewhat time lag from an instant when the output torque from the internal combustion engine is increased to an instant when the driven wheel torque is increased. For this reason, when the driven wheel torque exceeds the required torque, the driven wheel is brought into a slipping state even if the driven wheel torque is controlled, and eventually, an on-off feed-back control around the required torque is conducted, thereby making it difficult to appropriately control the driven wheel torque.